alt Hacker NewsJust think about what "tests pass" means for a rewrite. If you rewrite from language A to language B then any unit tests have to be rewritten during the rewrite.
So either "tests pass" does not include unit tests or unit tests were rewritten probably by the same AI that is doing the rewrite!
The good part about a language runtime is there's a massive corpus of tests that are in that language and agnostic to the implementation language.
For a JS engine that's Test 262: https://github.com/tc39/test262
For node that's its unit tests which are mostly JS: https://github.com/nodejs/node/tree/main/test
Node also runs the web platform tests too: https://web-platform-tests.org/
Bun has a similar large corpus of JS/TS tests: https://github.com/oven-sh/bun/tree/main/test
You're right about general purpose rewrites, but language runtimes are a lot easier.